8,596 research outputs found
Analysis of SPAR 8 single-axis levitation experiment
The melting and resolidification of SPAR 8 payload melting and resolidification of a glass specimen from the in a containerless condition and the retrieval and examination of the specimen from the. The absence of container contact was assured by use of a single-axis acoustic levitation system. However, the sample contacted a wire cage after being held without container contact by the acoustic field for only approximately 87 seconds. At this time, the sample was still molten and, therefore, flowed aroung the wire and continued to adhere to it. An analysis of why the sample did not remain levitated free of container contact is presented. The experiment is described, and experimental observations are discussed and analyzed
Digital control of magnetic bearings supporting a multimass flexible rotor
The characteristics of magnetic bearings used to support a three mass flexible rotor operated at speeds up to 14,000 RPM are discussed. The magnetic components of the bearing are of a type reported in the literature previously, but the earlier analog controls were replaced by digital ones. Analog-to-digital and digital-to-analog converters and digital control software were installed in an AT&T PC. This PC-based digital controller was used to operate one of the magnetic bearings on the test rig. Basic proportional-derivative control was applied to the bearings, and the bearing stiffness and damping characteristics were evaluated. Particular attention is paid to the frequency dependent behavior of the stiffness and damping properties, and comparisons are made between the actual controllers and ideal proportional-derivative control
Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium
We present a theoretical study of transient absorption and reshaping of
extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately
strong infrared (IR) laser field. We formulate the atomic response using both
the frequency-dependent absorption cross section and a time-frequency approach
based on the time-dependent dipole induced by the light fields. The latter
approach can be used in cases when an ultrafast dressing pulse induces
transient effects, and/or when the atom exchanges energy with multiple
frequency components of the XUV field. We first characterize the dressed atom
response by calculating the frequency-dependent absorption cross section for
XUV energies between 20 and 24 eV for several dressing wavelengths between 400
and 2000 nm and intensities up to 10^12 W/cm^2. We find that for dressing
wavelengths near 1600 nm, there is an Autler-Townes splitting of the 1s ---> 2p
transition that can potentially lead to transparency for absorption of XUV
light tuned to this transition. We study the effect of this XUV transparency in
a macroscopic helium gas by incorporating the time-frequency approach into a
solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal
reshaping dynamics when a 61 fs XUV pulse resonant with the 1s ---> 2p
transition propagates through a helium gas dressed by an 11 fs, 1600 nm laser
pulse.Comment: 13 pages, 8 figures, 1 table, RevTeX4, revise
Universal Quantum Viscosity in a Unitary Fermi Gas
A Fermi gas of atoms with resonant interactions is predicted to obey
universal hydrodynamics, where the shear viscosity and other transport
coefficients are universal functions of the density and temperature. At low
temperatures, the viscosity has a universal quantum scale where
is the density, while at high temperatures the natural scale is
where is the thermal momentum. We employ breathing mode damping to
measure the shear viscosity at low temperature. At high temperature , we
employ anisotropic expansion of the cloud to find the viscosity, which exhibits
precise scaling. In both experiments, universal hydrodynamic
equations including friction and heating are used to extract the viscosity. We
estimate the ratio of the shear viscosity to the entropy density and compare to
that of a perfect fluid.Comment: 13 pages, 3 figure
Upper Holocene Paleoceanography of Inner Miramichi Bay
Changes in sediment texture and in foraminiferal and molluscan assemblages observed in three vibracores collected in Miramichi Inner Boy reflect the development of a barrier island system across the mouth of the Bayt and the opening and closing of channels between the islands. The barrier island system apparently developed initially between 4400 and 3600 C14 years B.P. Opening and infilling of Buckleberry Gulley during the past 1300 years is indicated by changes in the proportions of estuarine and open bay assemblages of benthonic foraminifera. Mollusc and foraminifera data do not always suggest the same paleoenvironmental conditions at any given place and time, but they are in good agreement with respect to the direction of paleoenvironmental trends
Statistical Communication Theory
Contains reports on two research projects.Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)National Aeronautics and Space Administration (Grant NsG-496
Statistical Communication Theory
Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)National Aeronautics and Space Administration (Grant NsG-496)National Science Foundation (Grant GK-835
Secreted NS1 Aids in Dengue Virus Entry by Binding Heparan Sulfate
A large portion of the world’s population lives in an area where they are at risk of contracting Dengue Virus (DENV). While infection with DENV can result in a wide range of clinical manifestations, from flu-like symptoms to hemorrhagic shock, vascular leakage, and even death, no treatments currently exist. Previous studies have shown that higher levels of viral non-structural protein 1 (NS1) in the blood of infected patients correlate with more severe disease. NS1 has been shown to play many roles in the viral lifecycle, but the mechanisms by which NS1 executes these functions are unknown. Preliminary data from our lab suggest that NS1 facilitates DENV entrance into the cell, and previous studies have shown that secreted NS1 binds to heparan sulfate on the surface of cells. In this study a region of NS1 was identified that may be important for binding the cell surface through interactions with heparan sulfate and thus mediating virus entry. A mutagenic approach was used to investigate the role of this region of NS1 in cell binding and virus entry. This study seeks to better understand the mechanism by which NS1 binds the cell surface and aids in virus entry to identify antiviral targets
Generalized Parton Distributions in Full Lattice QCD
We present recent results on generalized parton distributions from dynamical
lattice QCD calculations. Our set of twelve different combinations of couplings
and quark masses allows for a preliminary study of the pion mass dependence of
the transverse nucleon structure.Comment: 8 pages, 5 figures; Talk presented by Ph.H. at Light-Cone 2004,
Amsterdam, 16 - 20 Augus
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